1. Field of the Invention
The present invention relates to a porous titanium oxide powder and a method of manufacturing the same, and further relates to the ultraviolet-protecting ability, usability, transparency and so on of the porous titanium oxide powder.
2. Description of the Related Art
Titanium oxide has a high refractive index, and has excellent concealing ability, coloring ability and ultraviolet-protecting ability, and has thus been widely used from hitherto as a pigment in paints, plastics, cosmetics and so on. As the titanium oxide contained in bases for such products as an ultraviolet-protecting agent, fine particle powders having a mean primary particle diameter of not more than 0.1 μm have come to be predominantly used, this being as a result of striving for good ultraviolet-protecting ability and transparency.
As methods of manufacturing titanium oxide, a method in which titanyl sulfate or titanium tetrachloride is heated and thus hydrolyzed in an aqueous phase, a method in which neutralization and hydrolysis are carried out and soon are known (see, for example, Japanese Patent Application Laid-open No. 55-10428).
However, a fine particle powder has a very small particle diameter, and hence the oil absorption amount is high, and thus agglomeration readily occurs, and hence dispersion in a product base system has been difficult. Moreover, cosmetics and so on containing such a fine particle powder have had a high UV-B region (290 to 320 nm) ultraviolet-protecting effect, but have had a low protection effect against UV-A region (320 to 400 nm) ultraviolet rays, and moreover there have been problems in actual use such as graininess and poor spreadability.
Due to such a state of affairs, to improve the dispersibility and the UV-A protecting ability, a fan-shaped titanium oxide powder in which are agglomerated acicular titanium dioxide primary particles has been proposed (see, for example, Japanese Patent Application Laid-open No. 10-245228).
However, with such particles, an improvement in the UV-A protecting ability can be recognized, but problems have remained in terms of usability.
Moreover, because titanium oxide has a high refractive index, there has been a problem of the transparency being poor compared with zinc oxide and so on.